Previous studies from our laboratory characterized a fearful/anxious endophenotype in rhesus monkeys that is. relevant to understanding normal human anxiety, as well as anxiety disorders. During the last funding period, we established a technique to selectively and reliably lesion the primate amygdala with ibotenic acid. The investigators' data are among the first to use modern lesioning techniques with sophisticated behavioral measures to address mechanisms underlying emotional processing in primates. Results demonstrate an important role for the amygdala in the processing of acutely fearful stimuli but a lack of amygdala involvement in mediating the dispositional behavioral, emotional, and physiological characteristics associated with fearful/anxious temperament. Orbitofrontal regions are bi-directional linked with the amygdala and the proposed studies will examine the role of orbitofrontal cortex in emotional processing, as well as the functional interaction between the amygdala and orbitofrontal cortex. Using ibotenic acid lesions and positron emission tomography, the investigators will explore the hypothesis that right orbitofrontal regions are primarily involved in mediating the behavioral and emotional responses associated with fearful/anxious temperament. The findings from these studies will be highly relevant to humans, addressing the role of amygdala orbitofrontal interactions in mediating normal emotion and psychopathology.